Abstract: Organic salt kappa-(BETS)(2)FeBr4 is a unique compound in which local moment antiferromagnetism of Fe3+ ions (below Neel temperature T-N of 2.5 K) coexists with bulk superconductivity (below the superconducting transition temperature T-C = 1.1 K). To probe this unique coexistence we studied the low-temperature far-infrared optical response in a frequency range of 7-40 cm(-1), a characteristic energy range for superconducting and magnetic gaps. Measurements were undertaken using a polarizing interferometer and a He-3 cryostat in a temperature range 0.5-2.8 K. The spectrum shows a clear change on crossing both T-N and T-C. An absorption feature below T-N is interpreted as a signature for the formation of a magnetic pseudogap. The observed increased reflectance relative to the normal state at temperatures below T-C sets a value of the superconducting energy gap Delta(0) in the strong coupling regime, 2 Delta(0) approximate to 8k(b)T(C).
Abstract: The 2 : 1 cation radical salts of bent donor molecules of ethylenedithio-tetrathiafulvalenoquinone-1,3- dithiolemethide (EDT-TTFVO), ethylenedithio-diselenadithiafulvalenoquinone-1,3- dithiolemethide (EDT-DSDTFVO), ethylenedithio-diselenadithiafulvalenothioquinone-1,3- diselenolemethide (EDT-DSDTFVSDS), ethylenedioxy-tetrathiafulvalenoquinone-1,3- dithiolemethide (EDO-TTFVO) and ethylenedioxy-tetrathiafulvalenoquinone-1,3- diselenolemethide (EDO-TTFVODS) with FeX4- (X = Cl, Br) ions are prepared by electrocrystallization. The crystal structures of these salts are composed of alternately stacked donor molecule and magnetic anion layers. The band structures of the donor molecule layers are calculated using the overlap integrals between neighboring donor molecules and are compared with the observed electronic transport properties. The magnetic ordering of the Fe(III) d spins of FeX4- ions is determined from magnetization and heat capacity measurements. The magnetic ordering temperatures are estimated by considering a combination of a direct d-d interaction between the d spins and an indirect pi-d interaction between the conduction pi electron and the d spins, whose magnitudes are separately calculated from the crystal structures with an extended Huckel molecular orbital method. The occurrence of a pi-d interaction is proved by the negative magnetoresistance, and the magnitude of magnetoresistance reflects the strength of the pi-d interaction. The effect of pressure on the magnetoresistance is studied, and the result indicates that the magnitude of magnetoresistance increases, namely, the pi-d interaction is enhanced with increasing pressure. From these experimental results it is shown that (EDT-TTFVO)(2)center dot FeBr4 is a ferromagnetic semiconductor, (EDT-DSDTFVO)(2)center dot FeX4 (X = Cl, Br) and (EDT-DSDTFVSDS)(2)center dot FeBr4 are metals exhibiting antiferromagnetic ordering of the d spins, and (EDO-TTFVO)(2)center dot FeCl4 and (EDO-TTFVODS)(2)center dot FeBr4 center dot(DCE)(0.5) (DCE = 1,2-dichloroethane) are genuine antiferromagnetic metals. Among them, the (EDT-TTFVO)(2)center dot FeBr4 salt is the first pi-d molecular system where the d spins of FeBr4- ions are ferromagnetically ordered through antiferromagnetic interaction with the conduction pi electrons. Corresponding to this ferromagnetic ordering, an anomalous dielectric slow-down phenomenon toward the ordering temperature is observed. The pi-d interaction in (EDT-DSDTFVSDS)(2)center dot FeBr4 is very large and comparable to that in pi-(BETS)(2)center dot FeCl4, which has the highest reported value so far, while the d-d interaction is fairly small. Concerning the ratio between the magnitudes of pi-d and d-d interactions (J(pi d)/J(dd)), this salt is currently the best pi-d molecular system.
Abstract: Electrochemical oxidation of a bent donor molecule ethylenedioxy-ethylenediseleno-tetrathiafulvaleno-thioquinone-1,3-dithio lemethide (EDO-EDSe-TTFVS, 1) and the corresponding quinone derivative EDO-EDSe-TTFVO (2) in the presence of (Bu4N)MCl4 (M Ga, Fe) affords single crystals of three radical cation salts, 1(2)FeCl(4), 1(2)GaCl(4), and 2(2)FeCl(4)(DCE) (DCE 1,2-dichloroethane). All of these salts exhibit semiconductor-to-semiconductor first-order phase transitions with a relatively large thermal hysteresis width (>15 K). The d-spins of FeCl4- ions in both 1(2)FeCl(4) and 2(2)FeCl(4)(DCE) show relatively strong antiferromagnetic interactions with Weiss temperatures of -7.1 and -9.2 K, respectively. The antiferromagnetic interaction in both salts originates from the preferential d-pi-pi-d interaction. The crystal structures of both 1(2)FeCl(4) and 1(2)GaCl(4) are solved at 298 and 150 K, which correspond to the high- and low-temperature phases (H- and L-phases), respectively. In each phase, the crystal structures of 1(2)FeCl(4) and 1(2)GaCl(4) are isomorphous. The donor molecules in the H- and L-phases of 1(2)FeCl(4) have similar packing patterns composed of one-dimensional columns with donor dimers. The phase transition of 1(2)FeCl(4) is accompanied by a slight orientational change of donor molecules in a dimer, and the electron correlation is enhanced on cooling. On the basis of the âmolecular coordinatesâ, the effect of the molecular rotation on the electronic phase transition is discussed. The results indicate that a slight molecular rotation can give rise to a significant change of electron correlation even in an electronic system with strong intermolecular interactions.
Abstract: The bimetallic Ru2Pt complex [((CpRu)-Ru-star)(2)(mu(2)-NHPh)(mu(2)-H)(mu(3)-C)PtMe(PMe3)(2)][OTf ] (3; Cp-star = eta(5)-C5Me5) containing a planar three-coordinate carbido ligand has been prepared in 93% yield by thermal isomerization of the bridging methylene precursor [((CpRu)-Ru-star)(2)Me(mu(3)-NPh)(mu(2)-CH2)Pt(PMe3)(2)][OTf] (2) via cleavage of the methylene C-H bonds. Exposure of the carbido complex 3 to carbon monoxide (1 atm) induced coupling of the carbido ligand with the nearby methyl and hydride ligands to produce the diruthenium ethylidene complex [((CpRu)-Ru-star)(2)(mu(2)-CHMe)(mu(2)-NHPh)(CO)(2)][OTf] (4) and the known triplatinum complex [Pt(CO)(PMe3)](3). The crystal structures of 2, 3, and 4 (BPh4 salt) are reported.
Abstract: We fabricated Au-TTF-Au (tetrathiafulvalene, TTF) and Au-TSF-Au (tetraselenafulvalene, TSF) single-molecule junctions using a nanofabricated mechanically controllable break junction. We found that Au-TSF-Au and Au-TTF-Au single-molecule junctions have one and two stable configurations, respectively, and that the Au-TTF-Au single-molecule conductance is Larger than that of Au-TSF-Au. The difference in single-molecule conductances of the two types of junctions originates from the difference in the strength of the molecule-electrode coupling through face-to-face overlapping configurations.
Abstract: Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide (2), in chlorobenzene (PhCl)/ethanol containing NBu4FeCl4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2(6) center dot Fe2OCl6 center dot 2PhCl are obtained that have a different molecular formula from that of 2(2) center dot FeCl4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe2OCl62- ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi(p)) observed can be described by the sum of chi(p) obeying a Curie-Weiss law for the impurity spins and of chi(p) obeying a dimer model with a spin-exchange integral (J similar to -180 K) in each Fe2OCl62- ion, which is also weakly coupled to neighboring Fe2OCl62- ions through an additional exchange interaction.
Abstract: Electronic properties of the pi-d system beta-(EDT-DSDTFVSDS)(2)FeBr4 are investigated, where EDT-DSDTFVSDS = ethylenedithiodiselenadithiafulvalenothioquinone-1,3-diselenolemethide. Clear contrast between the FeBr4 salt and the nonmagnetic anion analogue salt, beta-(EDT-DSDTFVSDS)(2)GaBr4, was observed in the electrical resistance and magnetoresistance (MR). The FeBr4 salt exhibits a giant negative MR of 85% at 0.7K and 14T. Furthermore, MR of the FeBr4 salt has a deep and sharp dip anomaly associated with the spin flop of the d spin at around 1.8T below Neel temperature T-Nd = 3.3K. A model calculation, based on the assumption that antiferromagnetic arrangement of the d spins enhances an insulating state, qualitatively reproduced the experimental result. These results demonstrate the strong pi-d interaction in the FeBr4 salt. Further, it is remarkable that in the higher angle of magnetic field from the easy axis, two anomalies associated with spin flop were observed. This behavior is neither explained by the conventional three-dimensional Ising nor XY models. The magnetic susceptibility of the FeBr4 salt obeys the Curie-Weiss law without a peak, which is characteristic of the usual low-dimensional antiferromagnet at higher temperature than Neel temperature.
Abstract: Two kinds of (BTM-TTP)(2)SbF6 salts, where BTM-TTP is 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-5-(1,3-dithiol-2-ylidene )-1,3,4,6-tetrathiapentalene, have been prepared. X-ray structure analyses have revealed that needle-like and plate-like crystals have the so-called beta- and theta-type arrays of the donors, respectively. The beta-type salt exhibits metallic conducting behavior down to 5 K, while the theta-type salt is a semiconductor even at room temperature.
Abstract: Ethylenedioxy- and ethylenedithiodithiadiselenafulvalenedithiolates are subjected to sulfur-selenium exchange, in which one selenium atom in the molecular skeleton is replaced by an outside sulfur atom. The reaction of the exchanged dithiolates with 2-methylthio-1,3-dithiolylium ion gives the corresponding thioquinone-1,3-dithiolemethides as new donor molecules.
Abstract: For the development of magnetic molecular conductors, we succeeded in the synthesis of new pi-electron donors containing TTF (tetrathiafulvalene) or TTP (tetrathiapentalene) framework and a stable 2,2,5,5-tetramethylpyrrolin-1-yloxyl radical within a molecule and clarified the crystal structure and physical properties of these donors. We also discuss the conducting and magnetic properties of a TCNQF(4) complex of the synthesized TTF type donor.
Abstract: To obtain novel single-component molecular metals, we attempted to synthesize several cobalt complexes coordinated by TTF (tetrathiafulvalene)-type dithiolate ligands. We succeeded in the syntheses and structure determinations of ((Bu4N)-Bu-n)(2)[Co(chdt)(2)](2) (1), ((Bu4N)-Bu-n)(2) Co(dmdt)(2)](2) (2), (Co(dmdt)212 (3), and [Co(dt)(2)](2) (4) (chdt = cyclohexeno-TTF-dithiolate, dmdt = dimethyl-TTF-dithiolate, and dt = TTF-dithiolate). Structure analyses of complexes 1-4 revealed that two monomeric [Co < ligand >(2)](-) or [Co(ligand)(2)](0) units are connected by two Co-S bonds resulting in dimeric [Co < ligand >(2)](2)(2-) or [Co < ligand >(2)](2) molecules. Complex 1 has a cation-anion-intermingled structure and exhibited Curie-Weiss magnetic behavior with a large Curie constant (C = 2.02 K-center dot mu center dot mol(-1)) and weak antiferromagnetic interactions (theta = -8.3 K). Complex 2 also has a cation-anion-intermingled structure. However, the dimeric molecules are completely isolated by cations. Complexes 3 and 4 are single-component molecular crystals. The molecules of complex 3 form two-dimensional molecular stacking layers and exhibit a room-temperature conductivity of sigma(rt) = 1.2 x 10(-2) S center dot cm(-1) and an activation energy of E-a = 85 meV. The magnetic behavior is almost consistent with Curie-Weiss law, where the Curie constant and Weiss temperature are 8.7 x 10(-2) K center dot emu center dot mol(-1) and -0.85 K, respectively. Complex 4 has a rare chair form of the dimeric structure. The electrical conductivity was fairly large (sigma(rt) = 19 S center dot cm(-1)), and its temperature dependence was very small ((sigma K-0.55/sigma(rt) = ca. 1:10), although the measurements were performed on the compressed pellet sample. Complex 4 showed an almost constant paramagnetic susceptibility (chi(300) (K) = 3.5 x 10(-4) emu center dot mol(-1)) from 300 to 50 K. The band structure calculation of complex 4 suggested the metallic nature of the system. Complex 4 is a novel single-component molecular conductor with a dimeric molecular structure and essentially metallic properties down to very low temperatures.
Abstract: An organic conductor beta ââ-(EDO-TTFVODS)(2)FeBr4(DCE)(0.5), where EDO-TTFVODS is ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide and DCE is 1,2-dichloroethane, has been synthesized and is expected to have a strong pi-d interaction. It was found that the material is metallic down to about 4 K and shows a rather slight upturn of electrical resistivity rho below this temperature. Temperature dependence of rho in the slight upturn region is proportional to log T and weak negative magnetoresistance (-1.7%, 2 T) at 1.4 K also appears. Besides pi-d interaction screened by conducting electrons in this material, weak localization and Kondo effect are also possible to explain this negative magnetoresistance. Oscillatory behavior probably due to a quasi-two-dimensional (Q2D) Fermi surface was observed in the field-orientation dependence, and k(F)parallel to bâ was estimated to be 0.19 angstrom(-1). (C) 2008 Elsevier Masson SAS. All rights reserved.
Abstract: New donor-acceptor dyads containing tetrathiafulvalene (TTF) and 2,5-diphenyl-1,3,4-oxadiazole (PPD) moieties were synthesized to develop new photoconducting materials. Crystal structure analysis indicated the highly planar molecular skeleton of the dyad. Fluorescence from the PPD part was almost quenched by the intramolecular electron transfer from the TTF part to the PPD part. Photoelectrochemical measurements indicate that cathodic photocurrents can be generated from a thin film of the dyad spin-coated on ITO electrode. (C) 2008 Elsevier Ltd. All rights reserved.
Abstract: In order to investigate its electronic structure and the pi-d interaction, we studied magnetoresistance (MR) of beta ââ-(EDO-TTFVO)(2)FeCl4. In the course of experiment Shubnikov-de Haas (SdH) effect was found, which shows that this material is a 2D metal. Below 3.5 K (close to T-N), MR shows a dip anomaly near 8 T. The anomaly becomes more prominent and shifts slightly to higher field with lowering temperature. The dip anomaly may be caused by the transition from the antiferromagnetic to the paramagnetic states. In addition, SdH oscillations are clearly seen at 0.5 K, whose cross-sectional area corresponds to 13% of the first Brillouin zone. The mass of the pi-electrons is m* similar or equal to 3.3 m(e), which seems heavy as compared with non-magnetic organic conductors with similar cross-sectional areas, suggesting the enhancement of the mass due to magnetic interaction with the Fe 3d spins. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: Electron spin resonance (ESR) experiments on (Benzo-TTFVS)(2)FeBr4 have been done with 15.4 GHz microwave by using aligned four single crystals, where Benzo-TTFVS denotes a new donor molecule with benzo group, benzotetrathiafulvalenothioquinone-1,3-dithiolemethide. FeBr4 includes Fe(III) d electron spin and an antiferromagnetic ordering occurs below the temperature of T-N = 5.8 K. We consider that observed ESR signals originate from d electrons at Fe ions. The shifts in a g-value and the broadening of a line width due to the antiferromagnetic fluctuation are observed at higher temperatures than TN. The g-value and the line width for H vertical bar vertical bar b are different from those for other directions. The b direction is the direction of the pi-d interaction along which donor molecules and counter anions are stacked alternately. These results suggest that the strong fluctuation is related to the pi-d correlation. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: We observed magnetic orderings of Fe3+ d spins in the 1:1 salts of BEDT-TTFVS(O) with FeX4- (X = Br, Cl) ions by magnetization measurements up to 0.5 T in the temperature range down to OAK using a homemade pulsed magnet system combined with a He-3 cryostat. Although temperature dependences of the magnetic susceptibilities above 20 K obeyed a Curie-Weiss law with positive Weiss temperatures, the salts were not subjected to ferromagnetic ordering but to antiferromagnetic orderings except for (BEDT-TTFVS) (.) FeBr4. The Neel temperatures, T-N were determined to be 2.4, 1.0 and 0.8 K for (BEDT-TTFVO) (.) FeBr4, (BEDT-TTFVO) FeCl4 and (BEDT-TTFVS) (.) FeCl4, respectively. Below T-N, a clear magnetization jump due to the spin-flop was also observed. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: Series of new TTF and bis-TTF containing a thiophene ring as a substituent or as a spacer group were prepared by using a pall adium-catalyzed cross-coupling reaction from tributylstannyl-trimethyltetrathiafulvalene (tMeTTF-SnBu3) and different halogeno and dihalogenothiophene derivatives. The reducing power of each new precursor was determined by cyclic voltammetry. Radical cations salts and charge transfer complexes of the donors with TCNQ were prepared and characterized. The electrical conductivity of these materials was measured and discussed in terms of (electronic) structure. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: The 2:1 salts of a new bent donor molecule, ethylenedithiodiselenad ithiafulvalenocluinone- 1, 3-diselenolemethide (EDT-DSDT-FVODS) and either an FeBr4-, or a GaBr4- ion exhibit semiconducting properties and had small activation energies. The Fe-III d spins of the FeBr4- salt are initially subject to a strong antiferromagnetic interaction and afterward exhibited a weak ferromagnetism at 3.8 K With a very small remanent magnetization of ca. 4 x 10(-2) mu(B) and a spin-flop near 25 kOe along the intercolumnar direction.
Abstract: Crystals of the 2 : 1 salts of a new donor molecule, benzotetrathiafulvalenoquinone-1,3-dithiolemethide ( 4, Benzo-TTFVO) with magnetic FeX4- and non-magnetic GaX4- ( X = Cl, Br) ions, 4(2) center dot FeX4 and 4(2) center dot GaX4, are isostructural to each other and showed a beta-type packing of the donor molecules where they form a uniform-stacked structure with an interplanar distance of 3.50 angstrom. These salts exhibited metallic behavior down to 140 - 170 K, but at these temperatures (similar to TM-I) an abrupt increase in the resistivities (rho) occurred and thereafter semiconducting behavior with an activation energy of 40 - 100 meV was observed. A structural change in the donor column from uniform to tetramer-unit stacks was observed in the 4(2) center dot FeBr4 crystal before and after TM-I. By application of pressures up to 1.0 GPa, the metallic behavior in the higher temperature region was gradually strengthened and TM-I gradually became lower with increasing pressure, but the transitions could not be suppressed at all. In response to the metal semiconductor transition at TM-I, there was a sharp decrease in the paramagnetic susceptibility of the pi electron system, where the transition from Pauli paramagnetism due to the metal-conducting behavior to the spin singlet state caused by tetramer formation of the donor molecules was observed. In addition, the FeX4- ( X = Cl, Br) salts showed comparatively strong antiferromagnetic interactions between the Fe( III) d spins of the FeCl4- and FeBr4- ions ( Weiss temperature: -11 K for 4(2) center dot FeCl4 and -37 K for 4(2) center dot FeBr4), giving rise to antiferromagnetic orderings at 1.6 K for 4(2) center dot FeCl4 and 9.3 K for 4(2) center dot FeBr4. The magnitudes of the d - d and pi - d interactions in 4(2) center dot FeBr4 are calculated to be J(dd) = 2.06 K and J(pi d) = 2.32 K, respectively. The comparison of these J values with the other magnetic conductors based on our system suggests that the d - d interaction of 4(2) center dot FeBr4 is stronger than the pi - d interaction. Since the three-dimensional antiferromagnetic ordering appears at the comparatively high temperature of 9.3 K, there is an important contribution of the pi electrons to the antiferromagnetic ordering of the Fe( III) d spins in order to mediate the magnetic interaction between two-dimensional magnetic anion layers.
Abstract: Nanowires of molecule-based charge-transfer salts are prepared using two different processing techniques. Isolated [TTF][TCNQ] nanowires are grown by a simple adsorption in organic solution method on stainless steel conversion coatings, used as substrates. They are characterized by Raman spectroscopy and current - voltage measurements. Nanowire films of Per(2)[Au(mnt)(2)] and (EDT-TTFVO)(4)(FeCl4)(2) are electrodeposited on ( 001)- oriented silicon wafers, used as anodes. In the second case, growth as nanowires occurs after functionalizing the Si electrode with a phospholipidic membrane. Electrodeposited nanowire films are studied by various techniques, including electron microscopy, vibrational spectroscopies, X-ray photoelectron spectroscopy and conductivity measurements.
Abstract: We report the synthesis, crystal structures, thermal, IR, UV-vis, and magnetic properties of a series of divalent transition metal formates, [NH4][M(HCOO)(3)], where M = divalent Mn, Co, or Ni. They crystallize in the hexagonal chiral space group P6(3)22. The structure consists of octahedral metal centers connected by the anti-anti formate ligands, and the ammonium cations sit in the channels. The chiral structure is a framework with the rarely observed 4(9)center dot 6(6) topology, and the chirality is derived from the handedness imposed by the formate ligands around the metals and the presence of units with only one handedness. The thermal properties are characterized by a decomposition at ca. 200 degrees C. The three compounds exhibit an antiferromagnetic ground state at 8.4, 9.8, and 29.5 K for Mn, Co, and Ni, respectively. The last two display a weak spontaneous magnetization due to a small canting of the moments below the critical temperature, and the Co compound shows a further transition at lower temperatures. The isothermal magnetizations at 2 K show spin-flop fields of 600 Oe (Mn), 14 kOe (Co), and above 50 kOe (Ni) and a small hysteresis with a remnant magnetization of 25 cm(3) G mol(-1) (Co) and 50 cm(3) G mol(-1) (Ni) and coercive field of 400 Oe (Co) and 830 Oe (Ni).
Abstract: By the reaction of new donor molecules, bis(ethylenedithio)tetrathiafulvalenoquinone(-thioquinone)-1,3-dithiolem ethides [BEDT-TTFVO (1) and BEDT-TTFVS (2)] with FeX3 (X = Cl, Br) in CS2/CH3CN, 1:1 salts of 1 or 2 with an FeX4- ion (1 center dot FeX4 and 2 center dot FeX4) were obtained as black needle crystals. Their crystal structures are very similar to each other, in which the donor molecules are strongly dimerized and the dimers construct a one-dimensional uniform chain along the a axis, while the FeX4- ions are located at an open space surrounded by the neighboring donor molecules and also construct a one-dimensional uniform chain along the a axis. There are close contacts between the donor molecules and the FeX4- ions and significant differences in the contact distances among the four salts. All of the salts are semiconductors with room-temperature electrical conductivities of 10(-4)-10(-2) S cm(-1). The Fe(III) d spins of the FeX4- ions are subject to dominant ferromagnetic interaction through the participation of one of the singlet pi spins to form a short-range ferromagnetic d-spin chain. Such neighboring chains interact antiferromagnetically with each other through the singlet pi spins and are ordered at 1.0, 2.4, and 0.8 K for 1 center dot FeCl4, 1 center dot FeBr4, and 2 center dot FeCl4, respectively. On the other hand, the antiferromagnetic ordering occurred with some canted angle at 1.9 K to leave a small magnetization for 2 center dot FeBr4.
Abstract: Shubnikov-de Haas (SdH) oscillations are measured in the organic conductor, K-(BETS)(2)FeBr4. In the canted antiferromagnetic (CAF) phase (mu H-0 < mu H-0(c) = 5.2 T), hysteresis is clearly observed in both the background resistance and oscillation amplitude. The analyses of the Dingle temperatures in the CAF phase show that some disorder is induced in the down sweep from the field above Hr. A possible origin of the excess scattering is discussed.
Abstract: (TTP-PROXYL)FeCl4, where TTP-PROXYL is 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (TTP) incorporating the 2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PROXYL) radical, is a semiconductor with two kinds of localized spin systems, that is, the systems of organic radical spins and 3d spins of magnetic FeCl4- ions. The 7 spin of the TTP-PROXYL radical cation disappears due to dimerization but the chi T-value of 4.65 Kemu mol(-1) indicates the coexistence of high-spin Fe3+ (S = 5/2) and PROXYL radical (S = 1/2) ill this salt. (TTP-PROXYL)GaCl4 is isostructural to the FeCl4 salt and exhibited similar semiconducting properties.
Abstract: Three BDT-TTP [2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene] salts, (BDT-TTP)(3)[(MCl4)-Cl-II](EtOH)(x) (M = Co, Mn, and Zn; x approximate to 1.0) were prepared. These salts are almost isostructural to one another. The crystals are composed of BDT-TTP columns, âBDT-TTP tapesâ that occupy the interstitial positions between BDT-TTP columns [(MCl4)-Cl-II](2-) anions and the crystal solvents, respectively. These salts showed weakly metallic conducting behavior down to about 150 K. At low temperature, the resistivities increased gradually with decreasing temperature, but the systems retained fairly high conductivities even at around 30 K. The [Z(II)Cl(4)](2-) salt indicated temperature independent paramagnetism down to low temperature. While the susceptibilities of the [(CoCl4)-Cl-II](2-) and [(MnCl4)-Cl-II](2-) salts showed the coexistence of pi conduction electrons and localized high-spins of the magnetic Co-II and Mn-II atoms. no significant pi-d interaction was observed. Band structure calculations were performed with taking account of the possibility of inhomogeneous distribution of pi electrons over the crystallographically independent three BDT-TTP molecules. The system has wide and narrow one-dimensional bands that originate from BDT-TTP columns and tapes, respectively. However, due to the interaction between BDT-TTP columns and tapes, the system gave a unique two-dimensional electronic band. The calculated energy dispersion curves were consistent with the weakly metallic behavior of the systems.
Abstract: We report results of Se-77 NMR frequency shift in the normal state of the organic charge-transfer salt kappa-(BETS)(2)FeBr4 which shows magnetic field-induced superconductivity (FISC). From a simple mean-field analysis, we determined the field and the temperature dependences of the magnetization m(pi) of the pi conduction electrons on BETS molecules. We found that the Fe spins are antiferromagnetically coupled to the pi electrons and determined the exchange field to be J=-2.3 T/mu(B). The exchange field from the fully saturated Fe moments (5 mu(B)) is compensated by an external field of 12 T. This is close to the central field of the FISC phase, consistent with the Jaccarino-Peter local field-compensation mechanism for FISC [Phys. Rev. Lett. 9, 290 (1962)].
Abstract: The 1:1 FeBr4- salt of a newly synthesized donor, ethylenedioxytetrathiafulvalenothioquinone-1,3-dithiolemethide (EDO-TTFVS) was prepared by an electrochemical oxidation. A crystal structure analysis and investigations on conducting/magnetic properties cleared that this (EDO-TTFVS)center dot FeBr4 salt is a new antiferromagnetic semiconductor with a high Neel temperature of 15 K.
Abstract: To explore novel physical phenomena related to strong pi-d interaction, we measured the resistivity (rho) and magnetoresistance of the first organic ferrimagnetic pi-d system, (EDT-TTFVO)(2)FeBr4 under high pressures up to 8 GPa, where EDT-TTFVO denotes ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide. At ambient pressure, rho(T) exhibits resistivity minimum near T-min similar to 170 K followed by a gradual increase below it. With increasing pressure, T-min abruptly decreases till 4 GPa, beyond which it slightly increases. The increase of T-min above 4 GPa is discussed in terms of the enhancement of the pi-d interaction by applying pressure.
Abstract: The 2:1 salts of two selenium analogues of benzotetrathiafulvalenothioquinone-1,3-dithiolemethide (1), [2â(X = S, Se) and 3â(X = S)] with magnetic FeX4- and non-magnetic GaX4- (X = Cl, Br) ions were prepared, and their crystal structures and electrical conducting /magnetic properties were investigated.
Abstract: We have measured the electrical resistivities and magnetoresistances (MR) of (EDT-DSDTFVO)(2)X (X = FeCl4, GaCl4), where EDT-DSDTFVO stands for ethylenedithiodiselenadithiafulvalenothioquinone-1,3-dithiolemethide. These materials undergo gradual metal-insulator transitions at T-min = 52 K for FeCl4-salt and T-min = 30 K for GaCl4-salt, respectively. In spite of the similarity of the temperature dependence of the resistivity and its pressure effect, MR of both salts exhibit a clear contrast, i.e. FeCl4-salt shows negative and GaCl4, positive. Origin of the difference in the sign of MR between these salts are discussed in terms of the existence of pi-d interaction.
Abstract: The magnetoresistance (MR) for a new organic conductor, betaâ-(EDO-TTFVO)(2)FeCl4 which exhibits metallic temperature dependence of the resistivity down to 0.3 K, was studied. Remarkable and unusual features were found: isotropic MR below 3 T, dip anomaly below 3 K, and SdH effect above 17 T These features are discussed in terms of an interaction between the pi-electrons on the EDO-TTFVO donors and the d-spins on the magnetic FeCl4- ions.
Abstract: Magnetic torque of the two-dimensional organic superconductor, kappa-(BETS)(2)FeBr4 was measured at 30mK under field B up to 17.5 T. In B perpendicular to layers, the field dependence of the torque shows a step-like kink at 5.5 T, which corresponds to the transition from the canted antiferromagnetic (AF) to the paramagnetic state. In B vertical bar vertical bar a (magnetic easy axis), we observed very anomalous torque curves, which are probably reflecting the successive magnetic transitions of the Fe 3d spins. The angular dependence of the torque in the AF state is discussed in terms of the uniaxial magnetic anisotropy of the 3d moments. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: The first antiferromagnetic organic superconductor, kappa-(BETS)(2)FeBr4 [BETS = bis(ethylenedithio)tetraselenafulvalene], was developed in the search for novel magnetic molecular conductors. This salt shows successive antiferromagnetic and superconducting transitions at T-N = 2.5 K and T-c = 1.1 K, respectively, at ambient pressure. Specific heat measurements and anisotropic behavior of intraplanar conducting properties under applied magnetic fields prove the coexistence of the antiferromagnetic ordering and superconductivity below T-c. The combination of metamagnetism of the magnetic layer and superconductivity of the conduction layer, which makes this salt a dual-functional system, yields two characteristic magnetic field-induced superconducting states around 1.6 and 12.5 T in terms of the Jaccarino-Peter compensation effect. Systematic studies on both the chemical pressure effect by a halogen exchange in the alloy system kappa-(BETS)(2)FeBCl4-x and the physical pressure effect by an application of real pressures in kappa-(BETS)(2)FeBr4 were performed to discuss the pi-d interaction in the kappa-(BETS)(2)FeBr4 system.
Abstract: [Co-3(HCOO)(6)](CH3OH)(H2O) (1), the isostructural analogue of the porous magnet of coordination framework [Mn-3(HCOO)(6)](CH3OH)(H2O), and its desolvated form [Co-3(HCOO)(6)] (2) were prepared and characterized by X-ray and neutron diffraction methods, IR, thermal analyses, and BET, and their magnetic properties were measured. The parent compound, 1, crystallizes in the monoclinic system, space group P2(1)/c, a = 11.254(2) Angstrom, b = 9.832(1) Angstrom, c = 18.108(3) Angstrom, beta = 127.222(2)degrees, V = 1595.5(4) Angstrom(3), Z = 4, R1 = 0.0329 at 180 K. It possesses a unit cell volume that is 9% smaller than [Mn-3(HCOO)(6)](CH3OH)(H2O) due to the smaller radius of CO2+ ion. Compared with the parent compound 1, the desolvated compound 2 has slightly larger lattice with cell parameters of a = 11.2858(4) Angstrom, b = 9.8690(4) Angstrom, c = 18.1797(6) Angstrom, beta = 127.193(2)degrees, V = 1613.0(1) Angstrom(3), R1 = 0.0356 at 180 K. The cell parameters of 2, obtained from neutron powder data at 2 K, are a = 11.309(2) Angstrom, b = 9.869(1) Angstrom, c = 18.201(3) Angstrom, beta = 127.244(8)degrees, V = 1617.3(5) Angstrom(3). The pore volume reduces from 33% to 30% by replacing Mn by Co. The material exhibits a diamond framework based on Co-centered CoCo4 tetrahedral nodes, in which all metal ions have octahedral coordination geometry and all HCOO groups link the metal ions in syn-syn/anti modes. It displays thermal stability up to 270 degreesC. The compound easily loses guest molecules without loss of crystallinity, and it partly reabsorbs water from the atmosphere. Significant N-2 sorption was observed for the desolvated framework suggesting that the material possesses permanent porosity. The magnetic properties show a tendency to a 3D long-range magnetic ordering, probably antiferromagnetic with a spin canting arrangement below 2 K.
Abstract: The 1:1 salt of a new donor molecule, ethylenedithiotetrathiaful-valenothioquinone-ethylenedithio-1,3-dithiole methide (1), with FeBr4- ion, 1.FeBr4, was prepared and found to exhibit a room-temperature electrical conductivity of 4 x 10(-2) S cm(-1) and semiconducting behavior with an activation energy of 170 meV. The paramagnetic susceptibility obeyed the Curie-Weiss law with a Curie constant of 4.42 emu K mol(-1) and a Weiss temperature of +3.4 K, and below 15 K, this short-range ferromagnetic interaction increasingly extended to two- and/or three-dimensional interactions, eventually giving rise to a ferromagnetic ordering, whose temperature (T-C) was determined to be 1.8 +/- 0.2 K using a resonant circuit method. The magnetic field dependence of magnetization showed that the saturation of magnetization was accomplished at ca. 60 kOe and the saturated value was ca. 5 mu(B), which is very close to the value obtained only due to Fe(III) (S = 5/2) d spins of one FeBr4- ion.
Abstract: A new organic-inorganic hybrid, (TTF+)Fe-III(C2O4)Cl-2, displaying canted antiferromagnetism has been prepared and characterized, where the tetrathiafulvalene (TTF) molecules are face-to-face dimers and the anion is a one-dimensional coordination polymer (see Figure). Due to pi-d interactions through short S...Cl and S...O contacts a three-dimensional Neel state is stabilized at the high temperature of 20 K.
Abstract: The neutral nickel and gold complexes with bis(trifluoromethyl)tetrathiafulvalenedithiolate ligands, [M(hfdt)(2)] (M = Ni, Au) were prepared in order to examine the possibility of the development of single-component molecular conductors soluble in organic solvents. However, in contrast to the previous report, the crystals did not show any solubility in the usual organic solvents. On the other hand, the crystal structure analyses showed unique two-dimensional layered structures, despite that the single-component molecular conductors usually tend to take a compact three-dimensional molecular arrangement. Each layer is separated by the terminal CF3 groups to form the âCF3 bilayer structureâ. The shortest intermolecular F...F distance (3.018 Angstrom for [Ni(hfdt)(2)] and 2.862 Angstrom for [Au(hfdt)(2)]) is significantly longer than the van der Waals F...F distance (2.70 Angstrom) and the distribution of the frontier electrons is almost zero around the CF3 bilayer region. This is due to the strong F. F segregation effect, which will provide a useful way to control the molecular aggregation in the single-component molecular conductors. Extended-Huckel tight-binding band structure calculations and the ab initio local density approximation (LDA) band structure calculations were made for [Ni(hfdt)(2)], which explains the semiconducting and non-magnetic properties of the system. Extended-Huckel tight-binding band structure calculations were also made for [Au(hfdt)(2)]. The calculated band structure is consistent with the semiconducting and almost non-magnetic properties of [Au(hfdt)(2)].
Abstract: We report results of Se-77 NMR study for a newly found field-induced superconductor, kappa-(BETS)(2)FeBr4. The nuclear spin lattice relaxation rate (1/T-1) above 25 K has a linear relation with temperature, 1/T-1=aT+b, which can be analyzed in a framework of normal metal with dipolar fields from uncorrelated 3d local moments to the Se nuclei. However, 1/T-1 has an evident kink at 25 K and shows a remarkable decrease within a narrow temperature range of 2.5 K. Below 22.5 K, we found that 1/T-1 follows a power law 1/T(1)similar to T-1.43, although the material is still conductive. The temperature where 1/T-1 shows a kink agrees with the temperature where the temperature devivative of the resistivity d rho/dT diverses. We discuss a possible reconstruction of the electronic state, which may attain magnetic correlation below this temperature.
Abstract: Molecular conductors based on peri-ditellurium-bridged polyacene donor molecules 3,4-dimethylanthra[1,9-cd:4,10-câdâ]bis[1,2]ditellurole (2,3-DMTTeA) and 2,3,6,7-tetramethylnaphtho[1,8-cd:4,5-câdâ]bis[1,2]ditellurole (TMTTeN) were prepared. The crystal structure analyses of neutral 2,3-DMTTeA molecule and its cation radical salts revealed that these crystals involve an orientational disorder of the asymmetrical molecule, 2,3-DMTTeA, and that the intermolecular network through tellurium atoms is very strong and dominant in terms of the construction of the crystal frameworks. In the crystal of (TMTTeN)(2)M(CN)(2) (M = Ag and Au), the crystal structure analyses and the extended Huckel tight-binding band calculations indicated that these salts are quasi three-dimensional conductors. These salts are highly conductive (720-760 S cm(-1)) and maintain metallic states down to about 50 K. Furthermore, the Ag(CN)(2)(-) salt exhibited a Pauli paramagnetic behavior down to 2 K [chi(para) approximate to 2.0-2.5 x 10(-4) emu mol(-1)], In the crystal of (TMTTeN)(SCN)(0.88), the donor molecules are stacked to form one-dimensional columns and construct a three-dimensional network between the columns through the intermolecular (TeTe)-Te-... contacts. The SCN- salt is also highly conductive (590 S cm(-1)) and maintains a metallic behavior down to 4.2 K. Almost temperature-independent paramagnetic susceptibility of (TMTTeN)(SCN)(0.88) indicates Pauli paramagnetism of this salt [chi(para) approximate to 1.6-1.9 x 10(-4) emu mol(-1)]. A tight-binding band structure calculation indicates that the Fermi surface of the SCN- salt is open along the b* and c* directions, but the intermolecular interactions between the donor columns are not so weak because of the three-dimensional network mediated by the protruded tellurium atoms. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Abstract: In order to investigate molecular conductors containing magnetic anions, pi d-interactions J(pi d) and dd-interactions id, have been estimated from the overlap of molecular orbitals by using the relation J = -2t(2)/U. In the present paper this method is applied to a new antiferromagnetic superconductor (BDA-TTP)(2)FeCl4, a semiconducting ferrimagnet (EDT-TTF-VO)(2)FeBr4, and a betaâ-type semiconductor (BEDT-TTF)(3)(MnCl4)(2). The dd interaction of (BDA-TTP)(2)FeCl4 is as large as lambda-(BETS)(2)FeCl4, guaranteeing the relatively high T-N. The small J(pi d) of this compound is related to the steric effect of the outer trimethylene groups of the donor. The observed ferrimagnetism in (EDT-TTF-VO)(2)FeBr4 is related to the localization of the pi-electrons associated with the charge order, as well as the fairy large pi d-interactions bridging different anions. (BEDT-TTF)(3)(MnCl4)(2) is a characteristic compound due to the extraordinarily large pi d-interactions to the donors incorporated in the anion layer. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: The 2 : 1 salts of a new donor molecule, benzotetrathiafulvalenothioquinone-1,3-dithiolemethide (Benzo-TTFVS) with magnetic FeCl4- and FeBr4- ions, and with non-magnetic GaCl4- and GaBr4- ions were obtained as single crystals by an electrochemical oxidation method. All of the crystals have very similar structures to each other, in which two different layers of the donor molecules and the counteranions are stacked alternately, although the separation distance between the neighboring donor layers in the FeCl4- and GaCl4- salts is shorter by 0.43-0.47 angstrom than that in the FeBr4- and GaBr4- salts. The donor molecules formed a beta-like stacking structure with almost the same interplanar distances and effective overlaps along the stacking direction, such that these salts showed high electrical conductivities (9-33 S cm(-1)) at room temperature, as well as metallic behavior. However, owing to a quasi one-dimensional character of the calculated band structures, a transition of metal-to-semiconductor with a very small activation energy of < 30 meV occurred at comparatively high temperatures of 100-150 K. The Fe(III) d spins of the FeCl4- ions were subject to weakly antiferromagnetic interaction (Weiss temperature, theta = -4.3 K). While, the interaction between the Fe(III) d spins of the FeBr4- ions was fairly strong (theta = -16.1 K), eventually giving rise to an antiferromagnetic ordering at the temperature of 5.8 K. In the magnetization measurement of the FeBr4- salt up to 320 kOe at 0.5 K, a spin-flop occurred near 20 kOe and a saturation near 156 kOe.
Abstract: Shubnikov-de Haas (SdH) and angular dependent magnetoresistance oscillations (AMROs) are measured in the organic superconductor with magnetic anions, kappa-(BETS)(2)FeBr4. In the paramagnetic phase (mu H-0>mu H-0(c)=5.5 T), the AMROs and the SdH oscillations are clearly observed, which are basically consistent with the band structure calculation. In the canted antiferromagnetic phase (H < H-c), a low frequency SdH oscillation is observed. The observation of the oscillation is not interpreted by the simple FS reconstruction due to the long range order of the Fe 3d spins and implies that the strong correlation between the pi and d electrons modifies the reconstruction. No sign of the enhancement of the critical quantum fluctuation at H-c is observed in the SdH oscillations, the reason of which is also discussed.
Abstract: To contribute to the development of single-component molecular metals, several nickel complexes with cyclohexeno-condensed or ethylenedioxy-substituted TTF (tetrathiafulvalene) dithiolate ligands, (R4N)(n)[Ni(chdt)(2)] [R = Me, n = 2 (1); R = Bu-n, n = 1 (2); n = 0 (3)] and (R4N)(n)[Ni(eodt)(2)] [R = Me, n = 2 (4); R = Bu-n, n = 1 (5); n = 0 (6)], were prepared. X-ray structures were determined on the monoanionic species 2 and 5. The tetra-n-butylammonium complex of the monoanionic [Ni(chdt)21 (2) with a 1:1 composition revealed that its magnetic susceptibility gave a good agreement with the Bonner-Fisher model (J/k(B) = -28 K), which was derived from the one-dimensional chains of anions with a regular interval. On the other hand, the magnetic susceptibility of the tetra-n-butylammonium complex of the monoanionic [Ni(eodt)(2)] (5) showed the Curie-Weiss behavior (C = 0.376 K(.)emu(.)mol(-1) and Theta = -4.6 K). Both of the monoanionic species 2 and 5 indicate that they belong to the S = 1/2 magnetic system and have relatively large and anisotropic g-values, suggesting the contribution of the nickel 3d orbital. Electrical resistivity measurements were performed on the compressed pellets of the neutral species 3 and 6. Fairly large conductivities were obtained (sigma(n) = 1-10 S(.)cm(-1)). In addition, despite the measurements on the compressed pellets of powder samples, the neutral species 6 showed metallic behavior down to ca. 120 K and retained high conductivity even at 0.6 K [sigma(0.6 K)/sigma(rt) approximate to 1/30], suggesting the crystal to be essentially metallic down to very low temperature. The electrical behavior and Pauli paramagnetism of 6 indicate the system to be a new single-component metal.
Abstract: Mn-3(HCOO)(6), a 3D highly stable and flexible porous diamondoid framework based on Mn-centered MnMn4 tetrahedral nodes, exhibits a wide spectrum of guest inclusion behaviour and long-range magnetic ordering with guest-modulated critical temperature.
Abstract: We synthesized pi-extended donors for magnetic conductors that contain a stable 2,2,5,5-tetramethylpyrrolin-1-yloxyl radical, and cleared their structure and physical properties. We also discussed the conducting and magnetic properties of cation radical salts of the synthesized donor.
Abstract: A series of new magnetic organic conductors consisting of pi donors with stable organic radical part and inorganic anions was prepared. The air-stable TTP derivatives containing a PROXYL radical were synthesized by phosphite-based cross-coupling reaction of 1,3-dithiol-2- one derivatives and the thione containing a PROXYL radical. The ClO4 and FeCl4 salts of TTP-PROXYL were electrochemically prepared. Besides the 2:1 salts with fairly high conductivity (D(2)A; D radical donor, A = anion), there is a semiconducting 1:1 complex (TTP-PROXYL)FeCl4 (sigma(RT) = 10(-3) Omega(-1) cm(-1), E-a = 0.12 eV). The temperature dependence of the susceptibilities suggests the coexistence of n-radical spins (S = 1/2) and Fe3+ magnetic moments (S = 5/2). The system with non-magnetic ions, (TTP-PROXYL) GaCl4 and (CpTTP-PROXYL)AsF6 salts were also examined.
Abstract: We synthesized pi-extended donors for magnetic conductors that contain a stable 2,2,5,5-tetramethylpyrrolin-1-yloxyl radical, and cleared their structure and physical properties. We also discussed the conducting and magnetic properties of cation radical salts of the synthesized donor.
Abstract: A stab I e -organic-radical-functionalized tetrathiapentalene organic conductor has been synthesized and studied using X-ray crystallography of very small single crystals. The crystal structure reveals alternating conducting and insulating layers (see Figure).
Abstract: The novel nickel complex with the extended-TTF dithiolate ligand [Ni(tmdt)(2)] (tmdt=trimethylene dithiotetrathiafulvalenedithiolate) is the first three-dimensional single-component molecular metal with metallic state down to very low temperature (0.6 K). Recently, the direct evidence for presence of electron and hole Fermi surfaces in [Ni(tmdt)(2)] was obtained by detecting the de Haars-van Alphen (dHvA) effect. We have synthesized analogous single-component molecular conductors with various ligands and central metal atoms and examined their structures and physical properties. The visible and ir spectra of single-component molecular conductors showed that these molecules have unprecedentedly small HOMO-LUMO gaps.
Abstract: In order to investigate the Fermi surface of the quasi-two dimensional (Q2D) organic superconductor kappa-(BETS)(2)FeBr4, the Shubnikov-de Haas (SdH) oscillation and the angular-dependent magnetoresistance oscillation (AMRO) have been measured. In the antiferromagnetic (AF) state, we observed the SdH oscillation with the low frequency of about 62 T that has not been ever reported. This new frequency can be ascribed to a small pocket formed by the reconstruction of the Fermi surface (FS) due to the long range AF order. In the AMRO, clear periodic oscillation as a function of tan theta was found. The oscillation shows the presence of a 2D FS as predicted by band calculations. The analyses of the periodicity indicate that the cross-section of the FS has an elliptic shape. In the magnetic field almost parallel to the layers, a peak in the resistance is observed, suggesting the coherent transport in the interlayer direction. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: The temperature-pressure phase diagram of the first antiferromagnetic organic superconductor kappa-(BETS)(2)FeBr4 shows that the Neel temperature increases with pressure, while the superconducting transition temperature decreases rapidly around 3 kbar.
Abstract: High field electronic state of the quasi-two dimensional organic Superconductor, kappa-(BETS)(2)FeBr4 Was investigated. Under the magnetic field exactly parallel to the conducting layers, zero resistance was observed in the region of about 11 similar to 14 T at 27 mK. This is the strong evidence of the field induced superconductivity in this salt. In the antiferromagnetic state below 5 T, Shubnikov-de Haas oscillation with a low frequency of 62 T was observed. This new frequency can be ascribed to a small pocket formed by the reconstruction of the Fermi surface due to the antiferromagnetic order.
Abstract: We report the synthesis, structures and physical properties of new TEMPO-containing electron donors in which a TEMPO radical part connects to the EDT-TTF (1) or EDO-TTF (2) skeletons through a pyrrolidine ring. The donors are paramagnetic and showed a slight antiferromagnetic interaction at low temperature region. The CV measurement showed two pairs of reversible redox waves originated from the TTF part and one oxidation wave from the TEMPO radical part. Physical properties of the iodine complex of 1 are also presented. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: The physical properties of BETS (=bis(ethylenedithio)tetraselenafulvalene) conductors with tetrahalide magnetic anions and related systems were investigated. We have recently succeeded to find the superconducting transition of the crystal of kappa-type TICl4- salt coated with epoxy resin (T-c(onset) = 2.5 K). The specific heat measurements on the antiferromagnetic organic superconductor, kappa-(BETS)(2)FeCl4 was performed down to 60 mK, which gave sharp peak at 0.45 K (T-N). The peak trails a tail at T > T-N, suggesting low-dimensionality of the spin system. Resistivity measurements under magnetic field of lambda-(BETS)(2)FeGa1-xCl4 (x approximate to 0.4) exhibiting superconductor-to-insulating (SC-I) transition, I-SC phase transition was observed around 4 T at T < 3 K. The âlow-field superconducting regionâ between metallic and insulating phases around zero magnetic field is connected with the âhigh-field superconducting regionâ. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: We report study of thermal conductivity of organic superconductors in magnetic field of varying orientation with respect to the conducting plane, paying special attention to the parallel case. At low temperatures the field dependence of thermal conductivity in this configuration shows notable difference from usual behavior, both for electronic and phononic contributions. We show that the behavior of the electronic thermal conductivity in organic superconductor lambda-(BETS)(2)GaCl4 is consistent with the formation of an inhomogeneous Fulde-Ferrel-Larkin-Ovchinnikov superconducting state. In a closely related antiferromagnetic superconductor K-(BETS)(2)FeBr4 interaction with magnetic sublattice leads to a first order transition at Hc(2) in parallel magnetic field and reentrant superconductivity at high fields. The phonon thermal conductivity is shown to be a good tool for picking up a dimensional crossover and lock-in transition in the vortex system.
Abstract: Electromagnetic properties of organic superconductors based on BETS [=bis(ethylenedithio)tetraselenafulvalene)] and MX4- (M=Fe, Ga; X=Cl, Br) were examined. Based on the results of resistivity measurements, the temperature-pressure-composition phase diagram of lambda-(BETS)(2)FexGa1-xBryCl4-y was determined. Due to the existence of Fe3+ ions, the crystal of lambda-(BETS)(2)FexGa1-xCl4 (x=0.4) exhibiting a superconductor-to-insulator transition showed an unprecedented resistivity behavior under magnetic field. lambda-(BETS)(2)Fe0.4Ga0.6Cl4 exhibited the successive insulatorâ>superconductorâ>metalâ>(field-induced) superconducting transitions with increasing the magnetic field parallel to the conduction plane up to 15 T and the insulatorâ>superconductorâ>metal transitions for the field perpendicular to the conduction plane. The magnetoresistance experiments on the first antiferromagnetic organic superconductor, kappa-(BETS)(2)FeBr4 down to 0.58 K disclosed an onset of field-induced superconducting transition around 12.5 T.
Abstract: A TTP donor containing a stable PROXYL radical was synthesized to develop conducting-magnetic bifunctional materials and its structure and physical properties were investigated. Furthermore its cation radical salts were prepared and revealed their conducting and magnetic properties.
Abstract: Molecular conductors on the basis of bis(ethylenedithio)tetraselenafulvalene (BETS) with tetrahedral anions TICl4-, MnBr42-, and CoCl42- were synthesized and studied by X-ray diffraction analysis. The salts under study exhibit various conducting properties: kappa-(BETS)(2)TICl4 (I) is a superconductor with T-c = 2.5 K, 0-(BETS)(4)MnBr(4)(.)2C(2)H(5)OH (II) is a metal up to approximate to30 K, while (BETS)(2)CoCl4 (III) is a dielectric. Salt I has kappa-packing of the donor molecules, salt II has 0-packing, whereas salt III has no conducting layers. These structural differences are mainly the reasons for different conducting properties of compounds I-III.
Abstract: The thermal conductivity of the antiferromagnetic organic superconductor kappa-(BETS)(2)FeBr4 was measured in oriented magnetic field. Both the antiferromagnetic state with T-N = 2.3 K and the superconducting state with T-N = 1.1 K are shown to be of bulk nature. In the parallel fields above 10 T the thermal conductivity shows an anomaly, being consistent with the formation of a reentrant superconducting state due to a Jaccarino-Peter effect. (C) 2003 Elsevier Science B.V. All rights reserved.
Abstract: We succeeded in the synthesis of several new donors containing a TTF moiety and a PROXYL radical within a single molecule for the development of magnetic conductors. We clarified the crystal structure and physical properties of these donors. The CV measurements revealed that both the donors showed one pair of one-electron reversible redox waves (E-1(1/2) : +0.49 and +0.57 V vs. Ag/AgCl, respectively) and one pair of broad two-electron reversible redox waves (E-2(1/2): +0.89 and +0.92 V, respectively). ESR spectra of the donors indicated three absorption lines (g =2.0059. a(N) = 14.2 G) characteristic of the PROXYL radical. The donors 1 and 2 are paramagnetic and showed antiferromagnetic interaction (theta =-2.1 and -8.7 K, respectively).
Abstract: Owing to the coupling between pi and d electron systems, organic conductors based on BETS molecules and magnetic anions such as FeCl4- and FeBr4- exhibit very unique physical properties. The orthorhombic kappa-(BETS)(2)FeBr4 system is the first antiferromagnetic organic superconductor. Due to the metamagnetic nature of Fe spin system, the magnetic field dependence of resistivity shows a strong anisotropy in the ac conduction plane below T-c. On the other hand, the triclinic modification, lambda-(BETS)(2)FeCl4 undergoes coupled antiferromagnefic and metal-insulator (MI) transitions at 8.5 K. The easy axis of the antiferromagnetic spin structure was found to be deviated from the c axis (parallel to needle axis of the crystal) by 30-35degrees. The field-induced insulator-to-metal transition and pressure-induced superconducting transition of lambda-(BETS)(2)FeCl4 were briefly described from the viewpoint of the role of coupling between pi and d electron systems. (C) 2002 Elsevier Science Ltd. All rights reserved.
Abstract: New stable molecular metals kappa-(BETS)(2)X.C2H4(OH)(2)(X = Br- (1) Cl- (2)) (BETS = bis(ethylenedithio)tetraselenafulvalene) were prepared and their full X-ray studies were performed. The crystals of 1 and 2 are isostructural to each other. BETS molecules form the K-type packing. The polymeric anion layers constructed of halogen atoms and ethylene glycol molecules included in the crystal have short contacts between halogen anions and oxygen atoms of the ethylene glycol molecules: Br...O, 3.27 (2)Angstrom Cl...O, 3.22(3) Angstrom. Temperature dependence of the electrical resistivities of I and 2 were metallic from room temperature down to 0.9 and 4.0 K. respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: Several conducting salts based on BETS [where BETS = bis(ethylenedithio)tetraselenafulvalene] molecules and divalent magnetic anions such as the (CoCl4)(2-), (CoBr4)(2-), and (MnBr4)(2-) were prepared. Electrocrystallization by using the (CoCl4)(2-) anion gave two kinds of crystals. Block-shaped crystals were cleared to be (BETS)(2)CoCl4, which is an insulator with the high-spin state of cobalt 3d spin. On the other hand, the X-ray crystal structure analysis of a plate-shaped crystal of the (CoCl4)(2-) salt revealed the system to be kappa-(BETS)(4)CoCl4(EtOH), which is metallic down to 0.7 K. The electronic band structure calculation gave a typical two-dimensional cylindrical Fermi surface. However, there is only very weak antiferromagnetic interaction between the S = (3)/(2) cobalt 3d spins because of its anion-solvent-intermingled layer structure. On the other hand, the electrocrystallization by using the (MnBr4)(2-) anion yielded the plate-shaped black crystals of the (MnBr4)(2-) salt. Crystal structure analysis of the (MnBr4)(2-) salt showed that the salt is theta-(BETS)(4)MnBr4(EtOH)(2) with alternating donor and anion-solvent mixed layers. The stacking direction in one donor layer is perpendicular to those of the neighboring layers. The electrical and magnetic properties of the theta-(BETS)(4)MnBr4(EtOH)(2) salt showed the metallic behavior down to similar to30 K and the paramagnetism of the high-spin manganese 3d spins. Band structure calculation of this salt gave an elliptical cylindrical Fermi surface. Because the Fermi surfaces of the adjacent donor layers are rotated to each other by 90degrees, the theta-(BETS)(4)MnBr4(EtOH)(2) salt becomes a two-dimensionally isotropic metal.
Abstract: Synthesis, structure and physical properties of novel pi-electron donors containing a TTF moiety and a PROXYL radical within a single molecule designed for the development of magnetic conductors are reported. We also clarified the physical proper-ties of the iodine complex of the ethylenedithio derivative.
Abstract: Crystals of BETS conductors containing FeX4- (X = Cl, Br) anions are polymorphic lambda-BETS2FeCl4 undergoes alpha pi-d coupled antiferromagnetic insulating transition at about 8.5 K. But it exhibits a paramagnetic metal - antiferromagnetic metal transition and superconducting transition at high pressure. kappa-BETS2FeX4 (X = Cl, Br) are antiferromagnetic organic superconductors with the transition temperatures of T-N 2.4 K (Br), 0.45 K (Cl) and T-c = 1.1 K (Br) and 0.1 K(Cl). Resistivity step observed at T-N is the first direct evidence for pi-d interaction in organic metals. No distinct anomaly in the specific heat at T-c and the anisotropy of the recovery of resistivity under magnetic field at T < T-c suggest the coexistence of superconductivity and magnetic order in λ-BETS2. FeBr4. In contrast to the case of κ-BETS2FeBr4 exhibiting three-dimensional magnetic transition, small entropy of the transition of κ-BETS(2)FeC1(4) indicates the low-dimensionality of the spin system.
Abstract: Among six BETS (=bis (ethylenedithio)tetraselenaful valene) superconductors, the systems with FeX4-(X=Cl, Br) anions exhibit salient electronic properties due to the coupling between pi and d electron systems. lambda-BETS2FeCl4 undergoes successive transitions as, antiferromagnetic insulating phase â> metallic phase with ferromagnetically oriented Fe3+ spins â> superconducting phase (H//conduction plane) â> metallic phase, with increasing magnetic field. kappa-BETS2FeX4. exhibits successive anti ferromagnetic and superconducting transitions with decreasing temperature. Resistivity anomaly observed at anti ferromagnetic transition temperature indicates an evidence for the Coupling between pi and d electron systems.
Abstract: Trimethyleneditelluro- and trimethyleneoxaditellitro-substituted dimethyl-TTF derivatives were prepared. The CV result of the trimethyleneditelluro-substituted dimethyl-TTF derivative shows characteristic multi-redox behavior and the trimethyleneoxaditelluro-substititted dimethyl-TTFderivative exhibits two pairs of reversible redox waves. The structures and physical properties of conducting salts based on their donors are also clarified.
Abstract: We have synthesized new electron donors in which one or two TEMPO radical parts connect to the TTF skeleton through a 1,3-dithiol-2-ylidene ring to prevent the steric hindrance of the bulky TEMPO radical for the purpose of the realization of metallic conductivity, Furthermore crystal structure and physical properties of the donors and the cation radical salt have been clarified.
Abstract: Magnetoresistance measurements have been performed for the organic conductor kappa-(BETS)(2) FeBr4 to investigate the Fermi surface. Three fundamental Shubnikov-de Haas oscillations (alpha, beta and gamma) were observed. The cross-sectional areas corresponding to the cc and P oscillations are about 20% and 100% in the first Brillouin zone, respectively. The oscillations can be assigned to the closed orbit and the magnetic breakdown orbit. The effective masses of the conduction electrons are determined to be 5.2m(0), for alpha and 7.9m(0) for beta. The heavy masses are probably due to the antiferromagnetic fluctuation effect of the Fe spins. The origin of the oscillation gamma with very low frequency is not explained by the band calculation. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: Recently we have studied the interplay between conductivity and magnetism by means of new organic donors containing a stable TEMPO radical. In this work, we have prepared a novel electron donor 1 in which a TEMPO radical part connects to the EDT-TTF skeleton through a pyrrolidine ring. The ESR spectra of 1 indicated three absorption lines (g =2.0062, aN = 15.5 G) characteristic of TEMPO radical, The donor 1 is paramagnetic and showed antiferromagnetic interaction at low temperature region (theta = -2.4 K). The CV measurement revealed 1 shows two pairs of reversible redox waves (+0.48 and +0.86 V vs. Ag/AgCl) and one oxidation wave (+0.83 V).
Abstract: The electrical and magnetic properties of kappa-(BETS)(2)FeBr4 salt [where BETS = bis(ethylenedithio)tetraselenafulvalene] showed that this system is the first antiferromagnetic organic metal at ambient pressure (T-N = 2.5 K). The characteristic field dependence of the magnetization at 2.0 K indicates a clear metamagnetic behavior. The small resistivity drop observed at T-N clearly shows the existence of the interaction between pi metal electrons and localized magnetic moments of Fe3+ ions. In addition, this system underwent a superconducting transition at 1.1 K. That is, kappa-(BETS)(2)FeBr4 is the first antiferromagnetic organic metal exhibiting a superconducting transition below Neel temperature. The magnetic field dependence of the superconducting critical temperature indicated that the superconductivity in this system is strongly anisotropic also in the conduction plane because of the existence of the metamagnetically induced internal field based on the antiferromagnetic ordering of the Fe3+ 3d spins in contrast to the cases of the other conventional organic superconductors. Furthermore, the specific heat measurement exhibited a lambda -type large peak of zero-field specific heat corresponding to the three-dimensional antiferromagnetic ordering of high-spin Fe3+ ions. The lack of distinct anomaly in the C-p vs T curve at T-c suggests the coexistence of the superconductivity and the antiferromagnetic order below T-c.
Abstract: We have recently found various magnetic organic conductors exhibiting novel electric and magnetic properties, where the interplay between magnetism and conductivity play an essential role. There are mainly two types of crystal modification (lambda and kappa) in (BETS)(2)FeX4 [BETS = bis(ethylenedithio)tetraselenafulvalene]. In the triclinic modification, lambda-(BETS)(2)FeCl4, conduction electrons in the BETS layers interact with spins localized on the FeCl4- anions to give an antiferromagnetic insulating ground state. But the system becomes a superconductor at high pressure. In addition, lambda-(BETS)(2)FexGa1-xCl4 (0.35 < x < 0.5) undergoes an unprecedented superconductor-to-insulator transition. The orthorhombic modification, kappa-(BETS)(2)FeBr4, has been revealed to be the first antiferromagnetic organic superconductor (T-N = 2.4 K and T-c= 1.1 K). The specific heat measurements showed evidence for the coexistence of magnetic order and superconductivity below T-c. The easy axis of the antiferromagnetic metal phase below T-N is parallel to the a axis and the field dependence of the magnetization showed a metamagnetic behavior around 2 T. Recently, we have found that isostructural lambda-(BETS)(2)FeCl4 under-goes similar magnetic and superconducting transitions at lower temperatures. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: A novel pyrazino-fused TSeF donor molecule 1 was synthesized. The donor 1 showed two pairs of reversible redox waves (+0.85 and +1.18 V vs. Ag/AgCl in PhCN). Many cation radical salts containing tetrahedral or octahedral anions showed metallic conducting behavior down to low temperature. Among them, the BF4- and ClO4- salts have unique donor arrangements, similar to the beta â -like structure and 2:1 donor-to-anion composition. These salts are two-dimensional conductors with a strong intermolecular interaction along the side-by-side direction of the donor molecule.
Abstract: The magnetic and thermal properties of an organic conductor incorporating localized magnetic moments, kappa-(BETS)(2)FeCl4, were investigated down to 60-70 mK, Similar to the Br analogue, kappa-(BETS)(2)FeBr4, kappa-(BETS)(2)FeCl4 exhibited successive antiferromagnetic and superconducting transitions with lowering temperature (T-N = 0.45 K, T-C= 0.1 K). That is, kappa-(BETS)(2)FeCl4 is the second antiferromagnetic organic metal that exhibits a superconducting transition at ambient pressure. It became clear that the halogen exchange (Br â> Cl) in the anions results in the strong reduction of both magnetic and superconducting transition temperatures. Resistivities showed a small drop at 0.45 K (= T-N), which gave a direct evidence of the existence of pi -d interaction between pi metal electrons and localized magnetic moments of Fe atoms. In contrast to kappa-(BETS)(2)FeBr4 exhibiting a three-dimensional nature of the magnetic transition, the specific heat of kappa-(BETS)(2)FeCl4 indicates the low dimensionality of the spin system. (C) 2001 academic Press.
Abstract: The SQUID measurements revealed an antiferromagnetic transition of kappa -BETS2FeBr4 around 2.5 K (BETS=bis(ethylenedithio)tetraselenafulvalene). Resistivity measurements showed an anomaly at T-N which gave a clear evidence for the interaction between pi metal electrons and localized magnetic moments in organic metal system for the first time. A superconducting transition was observed at 1.1 K. The specific heat indicates the coexistence of antiferromagnetism and superconductivity below T-c. Similar successive antiferromagnetic and superconducting transitions were observed in kappa -BETS2FeCl4. A superconducting transition was observed also in lambda -BETS2FeCl4 at high pressure.
Abstract: Three selenium analogues of DTEDT [2-(1,3-dithiol-2-ylidene)-5-[2-(1,3-dithiol-2-ylidene)ethylidene]-1 ,3,4,6-tetrathiapentalene] have been synthesized. They showed four pairs of single-electron redox waves. The E-1 values are a little higher by 0.02-0.05 V than that of DTEDT. On the other hand, the E-2-E-1 values are almost equal to that of DTEDT. Their TCNQ complex and cation radical salts show fairly high electrical conductivities and several salts exhibit metallic conductivities. In particular the ReO4- and Au(CN)(2)(-) salts of DTEDS and the SbF6-, TaF6- and I-3(-) salts of DSEDS exhibited stable metallic behaviour down to 1.5-4.2 K. An X-ray crystal structure analysis of the metallic salt (DSEDS)(3)TaF6 reveals that this salt has a two-dimensional beta-type packing motif of the donor molecules similar to the superconducting (DTEDT)(3)Au(CN)(2). The calculated Fermi surface of (DSEDS)(3)TaF6 is a two-dimensional closed ellipsoid.
Abstract: Similar to the recently discovered organic conductor kappa-(BETS)(2)FeBr4 exhibiting a transition from an antiferromagnetic metal phase to a superconducting phase at 1.0K, kappa-(BETS)(2)GaBr4 shows a super-conducting transition around 0.5-1.0K, indicating T-C of kappa-(BETS)(2)MBr4 (M = Fe, Ga) to be almost independent of the existence of magnetic anions; from these findings a way to develop novel organic conductors with controlled antiferromagnetic interactions is suggested.
Abstract: The ac magnetic measurements on an organic metal, kappa- (BETS)(2)FeCl4 down to 60 mK revealed successive antiferromagnetic and superconducting phase transitions at about 0.65 K (approximate to T-N) and 0.1 K (approximate to T-C), respectively. These transitions correspond to the similar transitions in the Br-analogue, kappa-(BETS)(2)FeBr4 but the transition temperatures of FeCl4 system are significantly lower than those of FeBr4 system (T-N = 2.5 K; T-C = 1.1 K).
Abstract: An organic conductor with a stable metallic state derived from its quasi-2D Fermi surface is reported. Pyrazinoethylenedithio-TTF is known to form a 2D network which should but does not facilitate conduction through intermolecular N-S and S-S contacts. The exchange of selenium for sulfur in these systems, discussed here, results in the formation of the desired metallic state.
Abstract: Several derivatives of tris-fused donors, 2-(1,3-dithiol-2-ylidene)-2â-(thiopyran-4-ylidene)-5,5â-bi(1,3,4,6-tetra thiapentalenylidene) (TPDT-TTPY) have been prepared. Cyclic voltammogram of the bis(n-hexylthio) derivative 1b showed four pairs of one-electron redox waves and a pair of two-electron redox one, which is in agreement with the existence of six redox-active sites. The first oxidation potential (E-1) of 1b (+0.35 V vs. SCE) is almost equal to that of the corresponding derivative of the bis-fused donor TPDT-TTP (6, +0.36 V). The E-2-E-1 values of 1b (0.21 V) is smaller by ca. 0.04 V compared with that of 6. The electrical conductivities of their conducting complexes are comparatively high (sigma(rt) = 10(-2) - 10(0) S.cm(-1)).
Abstract: Crystal structures and conducting properties of various cation-radical salts with peri-ditellurium bridges, 2,3-DMTTeA and TMITeN were examined. The electrical conductivity and the magnetic susceptibility measurements show that (TMTTeN)(2)Ag(CN)(2) is metallic down to low temperature. It is the first pure organic ii conductor having stable metallic state and quasi-3D tight-binding Fermi surfaces.
Abstract: A bis-fused pi-electron donor incorporating a pyran-4-ylidene moiety, 2-(1,3-dithiol-2-ylidene)-5-(pyran-4-ylidene)-1,3,4,6-tetrathiapentalene (PDT-TTP, 1a), and its derivatives (1b-d) have been synthesized. The cyclic voltammograms of PDT-TTPs are composed of three pairs of redox waves. Comparison of the first oxidation potentials (E-1) suggests PDT-TTP (+0.42 V vs SCE in benzonitrile) is a weaker donor than TTF (+0.35 V). The present donors have produced a large number of highly conducting (sigma(rt) = 10(0)- 10(2) S cm(-1)) molecular complexes. Among them, conducting salts based on the ET-PDT (1d) are metallic down to liquid helium temperature, The metallic PF6- salt of ET-PDT has a composition of(ET-PDT)(4)PF6(cn), where cn is 1-chloronaphthalene, in which two crystallographically independent ET-PDT molecules A and B form a face-to-face stack with a four-folded period as AâABBâ. In the present salt, the head-to-tail overlap of the unsymmetrical pi-electron framework of PDT-TTP prevents an effective intrastack overlap and produces a strongly dimerized electronic structure along the stack direction. Tight-binding band calculations indicate that it has opened Fermi surfaces characteristic of quasi-one-dimensional metals.
Abstract: In the search for new organic conductors based on tetrathiafulvalene (TTF) an unsymmetrical tellurocycle-fused TTF molecule is examined. The crystal structures and electrical properties of the charge-transfer complex and cation radical salts prepared from this donor molecule are also investigated. The Figure shows the donor-acceptor stacking of its complex with 7,7,8,8-tetracyanoquinodimethane (TCNQ).
Abstract: Recently interplay between conductivity and magnetism has been focused in the research of new organic conductors. In this work, novel electron donor TEMPOET which is consisted of the extended TTF skeleton and stable TEMPO radical part was synthesized. The ESR spectra of TEMPOET indicated three absorption lines (g = 2.0062, a(N) = 15.1 G) characteristic of the TEMPO radical. Tt is revealed that TEMPOET shows paramagnetic susceptibility corresponding to one spin per molecule and slightly antiferromagnetic interaction at low temperature region (theta = -1.00 K). The CV measurement revealed TEMPOET shows one pair of reversible redox waves (0.88 V vs. Ag/AgCl) and three pairs of irreversible ones (+0.56, +1.17, +1.77V).
Abstract: A novel organic electron donor containing a stable TEMPO radical (TEMPOET) was synthesized and its magnetic and electrochemical properties were investigated; furthermore, the crystal structure and physical properties of the Au(CN)(2)(-) salt of TEMPOET were clarified.
Abstract: A new stable organic metal, TMTTeN(SCN)(0.88), where TMTTeN is 2,3,6,7-tetramethylnaphtho[1,8-cd:4,5-câdâ]bis[1,2] ditellurole, was obtained. The donors are stacked to form columns and three-dimensional network is developed through Te ... Te contacts. The salt is highly conductive and keeps metallic behavior down to 4.2 K. Furthermore the salt exhibits Pauli paramagnetic behavior down to 2 K. The extended Huckel tight-binding band calculation was examined.
Abstract: We synthesized novel TTF dimer molecules in which two TTF moieties are connected to each other by two trisulfide chains. Structure of tetrakis(methylthio) derivative 1 is cyclophane-like one and interplanar distance in the dimer is 3.86 Angstrom. 1 shows two pairs of reversible one-electron redox waves (+0.57 and +0.67 V vs. Ag/AgCl in PhCN) and one pair of reversible two-electron redox wave (+1.15 V). The ClO4- salt of 1 has 1:2 (Donor:Anion) composition and is an insulator. On the other hand the PF6- salt of bis(trimethylene) derivative 2 has one-dimensional columnar donor array with 1:1 composition and shows semiconducting behavior(sigma(rt)=10(-1) Scm(-1)).
Abstract: Several cation radical salts of an unsymmetrical donor, 2-cyclopentanylidene-1,3-dithiolo [4,5-d]-4â,5â-ethylenedithiotetrathiafulvalene (CPDTET) have been prepared. Most salts with octahedral (AsF6-, SbF6-, NbF6- and TaF6-) and linear (I-3(-)) anions showed high conductivity (sigma(rt) = 10(0)-10(2) S cm(-1)) and metallic conductive behaviour around room temperature. Among them, the AsF6- salt displayed metallic temperature dependence down to 4.2 K, while the SbF6- and TaF6- salts exhibited metal-to-semiconductor transitions at 200 and 140 K, respectively. The AsF6- and SbF6- salts have a kappa-type donor arrangement in which two donor molecules are strongly dimerized in a âhead-to-headâ manner. The calculated Fermi surfaces of these salts are two-dimensional folded circles. Measurement of the thermoelectric power suggests that the AsF6- salt is a normal metal, however, the SbF6- salt has an almost half-filled band structure at room temperature and a small energy gap opens at low temperature. The measurements of magnetic susceptibility indicate that these two salts exhibited Pauli-paramagnetic temperature independence characteristic of metallic materials, though they also showed weak antiferromagnetic interaction. The differences between AsF6- and SbF6- salts are also discussed and the origin of the metal-to-semiconductor transition is clarified.
Abstract: The first stable organic metals of the peri-ditellurium-bridged polyacene donor TMTTeN were obtained as TMTTeN2M(CN)(2) (M = Ag, Au). Crystal structure analyses revealed three-dimensional networks through intermolecular Te ... Te contacts. The salts are highly conductive (500-1000 S cm(-1)) and keep the metallic states down to low temperature. The extended Huckel tight-binding band calculation gave the quasi-three-dimensional Fermi surfaces.
Abstract: We have synthesized novel trisulfide-bridged tetrathiafulvalene (TTF) dimer molecule in which two TTF moieties are connected to each other by two trisulfide chains. X-Ray crystal structure analysis reveals that the molecule has a unique cyclophane-like U-shape structure. The structure of the ClO4, salt is also described.
Abstract: Several BDT-TTP derivatives fused with benzene (1a-e) and 1,2,5-thiadiazole (2c, f) rings have been synthesized. Their cation radical salts and TCNQ complexes show high conductivity (sigma(rt) = 10(-1)-10(3) S cm(-1)). Among them, ClO4 salt of 1d is metallic down to low temperature.
Abstract: Three selenium analogues of bis-fused donor DTEDT have been synthesized. They showed four pairs of single-electron redox waves. The E-1 values are a little higher by 0.02 - 0.05 V than that of DTEDT (+0.37 V). On the other hand, the E-2-E-1 values (0.12 - 0.13 V) are almost equal to that of DTEDT (0.13 V). TCNQ complex and cation radical salts of them show fairly high electrical conductivities (10(-1) - 10(2) S.cm(-1)) and several salts show metallic conducting behavior down to 1.5 - 4.2 K. An X-ray crystal structure analysis of a metallic salt (DSEDS)(3)TaF6 reveals that this salt has two-dimensional beta-type packing motif of donor molecules.
Abstract: Many cation radical salts based on BDT-TTPs substituted with both alkyl and methylthio groups have been prepared. Several salts showed metallic conductivity down to liquid helium temperature. Among them, X-ray structure analysis and band calculation of (CPTM-TTP)(4)AsF6 reveal that it has beta-type arrangement of donors and a closed Fermi surface.
Abstract: Several derivatives of alkyl-substituted DTEDT have been synthesized. Single crystals of cation radical salts of dimethyl-DTEDT (1Ab) with octahedral anions showed high conductivities (sigma(rt)=10(0)-10(1)Scm(-1)) and metal-like behavior around room temperature. The metal to insulator transition temperature tends to decrease as the volume of anions increases. The PF6, AsF6 salts of cyclopenteno-DTEDT (1Ac), and TaF6 salt of tetramethyl-DTEDT (1Bb) show metallic conducting behavior down to 50 K.
Abstract: A series of cyclopenteno annelated bis-fused TTF derivatives (CP-TTP 1a-d) have been synthesized. The present donors have produced many molecular complexes showing high conductivity. In particular, several cation radical salts based on the bis(methylthio)-(CPTM-TTP 1c) and ethylenedithio (CPET-TTP, 1d) derivatives are metallic down to liquid helium temperature, though resistivity of CPTM-TTP salts increases a little at low temperature. Among metallic salts, (CPTM-TTP)(4)X (X = PF6-, AsF6- and SbF6-) are isostructural and have two-dimensional ââbeta-typeâ arrangement of donor molecules. The band calculations of these salts indicate they have eclipsed Fermi surfaces characteristic of two-dimensional metals.
Abstract: The synthesis, structure and physical properties of the new selenium containing metal complex NBu4[Ni(ddds)(2)] (ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate) are described.
Abstract: A large number of radical-cation salts that retain metallic conductivity down to low temperatures have been prepared on the basis of bis-fused tetrathiafulvalene (TTF) donors. The stable states are associated with inherent tendency of these extended molecules to form two-dimensional conducting sheets. Structural and conducting properties of various TTP salts so far obtained are summarized.
Abstract: The first vinylog of bis-fused tetrathiafulvalene (DTEDT) has been synthesized as a new donor component for organic conductors. Many cation radical salts of DTEDT showed metallic conducting behavior down to liquid helium temperature regardless of counter anions. Further, (DTEDT)(3)Au(CN)(2) exhibited superconducting transition at 4 K under ambient pressure. X-Ray crystal structure analysis of (DTEDT)(3)Au(CN)(2) reveals that this salt has a ââuniform beta-typeâ arrangement of donor molecules in the conducting sheet. The band calculation indicates it has a closed Fermi surface.
Abstract: Anomalous conducting behavior in TTP series salts, particularly (CPTM-TTP)(4)PF6, where CPTM-TTP is 2-(4,5-cyclopenteno-1,3-dithiol-2-ylidene)-5-(4,5-dimethylthio-1 ,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, has been investigated in detail. This charge-transfer salt shows resistivity jumps around 100K, but is still metallic at low temperatures. These jumps are suppressed under applied pressures. Below 30K several sudden drops of resistivity like superconducting transitions are observed, but are not affected by magnetic fields. This anomalous behavior is discussed in view of hysteretic transitions between two metallic phases.
Abstract: Several cation radical salts of MeEtDTET, EtDTET and CPDTET were prepared. Many of them showed metallic conducting behavior down to 1.4-4.2 K. X-ray crystal structure analysis of (CPDTET)(2)(SbF6)(0.87) revealed that this salt has a two-dimensional ââkappa-typeâ arrangement of donor molecules.
Abstract: Bis-fused pi-electron donors composed of tetrathiafulvalene (TTF) and 2-(thiopyran-4-ylidene)-1,3-dithiole (TPDT), 2-(1,3-dithiol-2-ylidene)-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapenta lene (1a, TPDT-TTP), and its derivatives (1b-d, 2a-d) have been synthesized as donor components for organic conductors. An X-ray structure analysis of bis(methylthio)-1 (1c) revealed that the TPDT-TTP skeleton is almost planar except for the outer 1,3-dithiole ring, and that the crystal has a two-dimensional ââtheta-typeâ arrangement of molecules. The cyclic voltammograms of TPDT-TTPs exhibit four pairs of single-electron redox waves. The first oxidation potential (E(1)) of 1a (+0.37 V vs SCE, in PhCN) is comparable to that of TTF (+0.35 V) and is higher by 0.1 V than that of TPDT (+0.27 V). The observed substituent effect on E(1) values suggests that the first one-electron oxidation mainly occurs in the 2-(thiopyran-4-ylidene)-1,3-dithiole !TPDT) moiety. On the other hand, onsite coulombic repulsion estimated from the E(2) - E(1) value is lower than in TTF and TPDT. MNDO MO calculations reveal that all the sulfur atoms in the 1,3-dithiole rings have the same phase in the HOMO, a condition necessary for realization of effective transverse intermolecular interaction. The present donors have produced many charge-transfer complexes and cation radical salts showing relatively high conductivity (sigma(rt) = 10(-1) - 10(1) S cm(-1)), several of which display metallic temperature dependence.
Abstract: New pi-electron donors are being sought for the preparation of organic conductors. The first synthesis of bisfused pi-electron donors incorporating a heteroaromatic pi-electron spacer (see Figure) is reported. The electrochemical properties of 3a-e and 4a-e and the crystal structure of 3e ate presented, the results for the TCNQ complexes 3a and 4a confirming that the fusion of two donor units is a suitable strategy forthe development of highly conducting molecular complexes.
Abstract: Oligothiophene cation radical salts were first prepared by the electrochemical oxidation method employing large-sized anions PF6-, AsF6-, TaF6-, BF4- and GaCl4-. Several large-sized anions (AsF6-,TaF6- and GaCl4-) gave black-needle crystalline salts. All the salts showed semiconductive behavior with the electrical conductivities of 10(-4)-10(-6) S/cm. Electrical conductivity and spectroscopic measurements on the cation radical salts have suggested that oligothiophene moiety in the present salts is highly oxidized, as in oligothiophene doped with nitrosyl salt.
Abstract: Several derivatives of bis-fused donors, 2-(1,3-dithiol-2-ylidene)-5-(pyran-4-ylidene)- 1,3,4,6-tetrathiapentalene (PDT-TTP) and its thiopyran analogue (TPDT-TTP) have been prepared. Electrochemical properties of these donors were investigated by means of cyclic voltammetry and the X-ray crystal structure analysis was performed for bis(methylthio)-TPDT-TTP. The electrical conductivities of their TCNQ complexes and cation radical salts are fairly high (10(-1) - 10(2) S*cm(-1)), and several salts show metallic temperature dependence of conductivity.
Abstract: Several cation radical salts of MeDTET showed metallic conducting behavior down to low temperature. X-Ray crystal structure analysis of (MeDTET)(3)PF(6)TCE(x) reveals that the donors have ââkappa-typeâ arrangement in the conducting sheet. The results of ESR spectra are consistent with metallic conductivity.
Abstract: The title donor, CPTM-TTP (4,5-cyclopenteno-4â,5â-bis(methylthio)-2,5-bis(1,3-dithiol-2-ylidene)-1 ,3,4,6-tetrathiapentalene) has produced metallic cation radical salts with octahedral and linear anions. Among them, (CPTM-TTP)(4)AsF6 has a two-dimensional ââbeta-typeâ arrangement of donor molecules and a closed Fermi surface.
Abstract: A general synthetic method of his-fused TTF (BDT-TTP) donors has been developed. The parent BDT-TTP has yielded many cation radical salts showing metallic conducting property down to low temperature (less than or equal to 1.2 K). Crystal and electronic structures of (BDT-TTP)(2)SbF6 are also presented.
Abstract: Several derivatives of 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylide,3-dithiole)-1,3,4,6-tetrath iapentalene (1Aa, DTEDT), which is a vinylogue of bis-fused TTF (BDT-TTP) containing one 2,2â-ethanediylidenebis(1,3-dithiole) (2), have been synthesized. The cyclic voltammograms of the DTEDTs consist of four pairs of single-electron redox waves. Comparison of the first oxidation potentials (E(1)) reveals that donating ability of 1Aa is rather weaker than those of 2 and TTF, in spite of the extension of the apparent pi-conjugation. Substituent effects on the E(1) values suggest that the first one-electron oxidation occurs mainly in the vinylogous TTF moiety. The smaller E(2)-E(1) value of 1Aa compared with those of BDT-TTP, TTF and 2 suggests a decrease in the on-site coulombic repulsion in the dication. An X-ray structure analysis of the neutral 4,5-dimethyl-4â,5â-bis(methylthio) derivatives (1Be) reveals that the crystal has a so-called âK-type arrayâ of molecules. An MNDO molecular orbital calculation indicates that the sulfur atoms at the termini of the vinylogous 1,3-dithiole rings are out of phase with the other sulfur atoms in the HOMO. The present donors have produced many molecular complexes exhibiting high conductivity. In particular, all of the radical-cation salts based on 1Aa obtained so far exhibit metallic conducting behaviour down to 1.4-4.2 K, regardless of the counter-anions.
Abstract: Many cation radical salts of BDT-TTP (2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene) showed metallic conducting behavior down to 0.6-1.2 K. X-Ray crystal structure analysis of (BDT-TTP)(2)SbF6 revealed that this salt has a two-dimensional ââbeta-typeâ arrangement of donor molecules in the conducting sheet.
Abstract: The ClO4, BF4, and ReO4 salts of BDT-TTP, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, are isostructural, having uniform columns of the donor molecules. These salts are essentially metallic down to low temperatures, though the resistivity increases to some extent below 200 K. The thermoelectric power and ESR show simple metal-like behavior down to low temperatures.
Abstract: The title compounds (1) were prepared as the donor components for organic conductors. The molecular and crystal structures of bis(methylthio) derivative were determined by X-ray diffractional analysis. Among charge-transfer complexes and cation radical salts of 1 prepared so far, I3- salt of unsubstituted-1 and IBr2- salt of methylenedithio-1 showed metallic temperature dependence of conductivities.
Abstract: The synthesis and electrochemical properties of the title compound and its derivatives are described; the electrical properties of their charge-transfer complexes and cation radical salts are also presented.
Abstract: New TTF derivatives, bis(2-methylidene-1,3-dithiolo[4.5-d])tetrathiafulvalenes (BDT-TTFâs, 1), and their unsymmetrical derivatives, (2-methylidene-1,3-dithiolo[4,5-d])tetrathiafulvalenes (MeDT-TTFâs, 2, CpDT-TTFâs, 3) which are condensed with one or two 1,3-dithiol-2-ylidene moieties, were synthesized. The electrochemical properties of these donors were investigated by means of cyclic voltammetry. The X-ray structure of dimethylthio derivative of CpDT-TTF showed that the molecule is almost planar except for cyclopentane ring and there were shorter S ... S contacts than the sum of van der Waals radii. BDT-TTFâs formed charge-transfer complexes with TCNQF4 whose electrical conductivities were 10(-3)-10(-4) Scm-1. On the other hand, DT-TTFâs afforded several metallic cation radical salts, in particular, I3 and ClO4 salts of ethylenedithio-MeDT-TTF exhibited metallic behavior down to 0.5 K.
Abstract: The synthesis and properties of the unsymmetrical tetrathiafulvalenes condensed with 1,3-dithiol-2-ylidene moieties are described; the electrical properties of several cation radical salts are also presented.
